In large capacity optical fiber communication systems that use wavelength-division multiplex (WDM) technology, optical signals formed by a large number of optical sources of mutually different wavelengths are transmitted on a single optical fiber in the form of a WDM signal. Thus, a WDM signal includes a large number of channels of mutually different wavelengths, and the optical signals constituting the components of the WDM signals are transmitted through the respective channels in the form of signal components of the respective wavelengths. In such large-capacity optical fiber communication systems, optical switches are used for separating the optical signal component of a desired channel from the WDM signal transmitted through the optical fiber.